These three books will have you on your way to Reformation doctrine and piety, all for about $50.
1) The Holy Bible (Authorized Version). Read the Word. The Westminster Reference Bible contains extensive cross-references; taking the time to look up each cross-reference will tremendously deepen your familiarity with the holy Scripture and you will more clearly see “the heavenliness of the matter, the efficacy of the doctrine, the majesty of the style, the consent of all the parts, the scope of the whole (which is to give all glory to God), the full discovery it makes of the only way of man’s salvation, the many other incomparable excellencies, and the entire perfection thereof” (WCF 1.5). (Publisher: Trinitarian Bible Society; ISBN: 978-1-86228-149-3).
2) The Psalms of David in Metre. Sing the Word. The Psalms have a special place in the life of the Christian. The Book of Psalms is the hymnbook of the Church. These are the songs, and this is the praise, that the Lord Himself has put in our mouth, “he hath put a new song in my mouth, even praise unto our God” (Ps. 40:3). Singing Psalms is an element of worship: both corporate worship, and family or private worship. We ought to sing the Psalms not only every week on the Lord’s Day, but also daily in family (or individual) worship. Therefore we ought to be deeply familiar with the Psalms. It is no wonder why, then, when the Apostle extorts us to let the Word of Christ dwell in us richly, the means he prescribes is the singing of Psalms (Col. 3:16). The Psalms teach us about Christ (Lk. 24:44), and by singing them, the Word of Christ will dwell in us richly. The Psalms of David in Metre is an accurate translation of the Psalms in common meter which is very easy to sing to any common meter tune. The mobile app is also very useful: 1650 Split Leaf Psalter App (iOS App) (Android App). Lastly, here is An Introduction to the 1650 Psalter. (Publisher: Trinitarian Bible Society; ISBN: 978-1-86228-096-0).
3) The Westminster Confession of Faith. Understand the Word. The Westminster Confession of Faith is a helpful tool for understanding the Scriptures. It is an accurate summary of the major points of the Christian faith, and a careful study of it will, I believe, show that its doctrine is wholly agreeable to the Word of God. This edition contains the original Confession of Faith, Catechisms, Directories for Public and Family Worship, Solemn League and Covenant, National Covenant, Sum of Saving Knowledge, and the Form of Presbyterian Church Government. (Publisher: Free Presbyterian Publications; ISBN: 0-902506-08-0)
“There have been many objections urged against the use of Creeds and Confessions of Faith, at different periods, and with various degrees of skill or plausibility. It is not necessary either to enumerate all these objections or to answer them all, since many of them have sunk into oblivion, and others have already met sufficient refutation. Almost the only objection which is now urged with any degree of confidence, is that which accuses Confessions of usurping a position and authority due to divine truth alone. This objection itself has its origin in an erroneous view of what a Confession of Faith really is, and of what it is in which the necessity of a Confession being framed consists. The necessity for the formation of Confessions of Faith does not lie in the nature of the sacred truth revealed to man; but in the nature of the human mind itself. A Confession of Faith is not a revelation of divine truth—it is ‘not even a rule of faith and practice, but a help in both,’ to use the words of our own Confession, but it is a declaration of the manner in which any man, or number of men—any Christian or any Church—understands the truth which has been revealed. Its object is, therefore, not to teach divine truth; but to exhibit a clear, systematic, and intelligible declaration of our own sentiments, and to furnish the means of ascertaining the opinions of others, especially in religious controversies.” (Robert Shaw, The Reformed Faith: An Exposition of the Westminster Confession of Faith, p. 11)